Pumping system

ABSTRACT

This invention relates to a pumping system. The design of the system is such that bi-directional operation can be achieved using a significantly smaller and hence lighter unit than those currently available. It uses the direction of rotation of the drive shaft to control the opening and closure of the by-pass means for controllably returning the fluid to the first reservoir.

[0001] This invention relates to a pumping system

[0002] Conventionally, pumping systsms designed for two way operationhave a fluid return channel to allow fluid to flow back from one fluidstore to another. Generally, the return channel and the pump arecontrolled independently. An example of a control mechanism for a returnchannel is a solenoid valve, the size of which can be comparable to thatof the motor. The disadvantage of this arrangement is that incorporationof such a return channel and associated control mechanism greatlyincreases the size and weight of the pump.

[0003] According to the present invention, a pumping system comprises afirst reservoir and a second reservoir; a motor coupled to a driveshaft; a pump, driven by the drive shaft, for pumping fluid from thefirst reservoir to the second reservoir; and by-pass means forcontrollably returning fluid from the second reservoir to the firstreservoir; characterised by a clutch between the drive shaft and theby-pass means whereby rotation of the drive shaft in a first directiondrives the pump and disengages the clutch while the by-pass means isclosed, and rotation of the drive shaft in a second direction engagesthe clutch so that the by-pass means is opened.

[0004] In the present invention, the by-pass means operates undercontrol of the drive shaft, thereby removing the need for separatecontrol components and so reducing the size and weight or the pumpingsystem.

[0005] When rotating the drive shaft in the first direction of rotation,closing the by-pass means when driving the pump maximises the net rateof fluid transfer between the first reservoir and the second reservoirwhilst rotation in the second direction allows return of the fluid fromthe second reservoir to the first reservoir. This arrangement isparticularly convenient given that motors often exhibit greater torqueand power characteristics in one direction of rotation compared to theother.

[0006] Preferably, the by-pass means is adapted to be closed when themotor is idle.

[0007] This allows fluid in the second reservoir to be maintained at ahigher pressure than fluid in first reservoir when the motor is idle.

[0008] Preferably, the by-pass means comprises a by pass valve.

[0009] Preferably, the by-pass means comprises a cam-follower and a cam;wherein the clutch is operative between the drive shaft and the cam; andwhereby opening and closure of the by-pass means is controlled byengagement of the cam-follower with the cam and rotation of the driveshaft.

[0010] Preferably, the cam comprises an end stop, whereby rotation ofthe drive shaft in the second direction causes the end stop to reach thecam-follower after the by-pass means is opened, thereby restraining thecam.

[0011] In a preferred embodiment, the clutch comprises a flexibleresilient sleeve attached to the drive shaft and adapted to grip a shaftoperatively associated with the by-pass means when the drive shaft Isrotated in the second direction; and whereby rotation of the drive shaftin the first direction causes the sleeve to loosen from thesecond-mentioned shaft. Conveniently, the flexible resilient sleevecomprises a spring.

[0012] Alternatively, the clutch comprises two clutch plates; whereineach clutch plate comprises bevelled teeth; wherein one clutch plate issprung loaded; whereby rotation of the drive shaft in the firstdirection allows the bevelled teeth to pass over each other; and wherebyrotation of the drive shaft in the second direction causes the bevelledteeth to mesh.

[0013] Preferably, the by-pass means is housed within the pump.

[0014] Preferably, the pump comprises a swash plate pump.

[0015] One benefit of a swash plate pump is that it uses a single wayvalve, so nothing leaks back to the first reservoir when the motor stopsrotating. Nor is a gearbox required on the Motor, so reducing the sizeand noise generated in operation.

[0016] An example of a pumping system according to the invention willnow be described with references to the accompanying drawings in which:

[0017]FIG. 1 illustrates, schematically, a pumping system according tothe present invention;

[0018]FIG. 2 illustrates the pumping system of FIG. 1 in more detail;

[0019]FIGS. 3 and 4 illustrate the motion of a piston within itsrespective cylinder in the pumping system of FIG. 1;

[0020]FIG. 5 illustrates by-pass actuation in the example of FIG. 1;

[0021]FIG. 6 showes an alternative clutch arrangement.

[0022]FIG. 1 illustrates, schematically, a pumping system according tothe invention. A motor 1 is coupled to and drives a pump 2 which pumpsfluid from a fist reservoir 3 to a second reservoir 4. A by-passmechanism 5 controls the return of fluid from the second reservoir tothe first reservoir, when motor rotation is reversed, assuming higherpressure in the second reservoir.

[0023]FIG. 2 shows the pumping system of FIG. 1 in more detail. An outerhousing 6 of the pumping system is attached to a bulkhead 7 by athreaded mounting spigot 8 and a nut (not shown). The first reservoir 3is provided outside the housing 6 and fluid flows between the firstreservoir and the second reservoir 4 via an orifice in the threadedmounted spigot 8. The housing 6 contains the pump and the by-passmechanism. The pump comprises a swash plate 9 and two pistons 10, 11that run in two cylinders 12, 13. The swash plate engages the twopistons which move within their respective cylinders. The swash plateengages both pistons at diametrically opposed positions on the swashplate and each piston is held against the swash plate by a spring 14, 15respectively.

[0024] The motor 1 is attached to the housing 6. The motor is coupled toa drive shaft. 16 which in turn is coupled to the swash plate 9 via acoupling 17. The motor drives the swash plate which cause both pistons10, 11 to oscillate within their respective cylinders 12, 13.

[0025]FIGS. 3 and 4 show the motion of the piston 10 Within itsrespective cylinder 12, FIG. 3 shows an extreme of oscillation, theengaged position, where the piston is, as far as possible, driven in tothe cylinder by the swash plate 9. FIG. 4 shows the other extreme ofoscillation, the disengaged position, where the piston is, as far aspossible, driven out of the cylinder by the spring 14 acting against thepiston.

[0026] From the disengaged position, movement of the piston 10 towardsthe engaged position causes the piston to compress fluid within thecylinder 12, the fluid having been received from the first reservoir 3via an inlet 18. Once the piston has moved past the inlet, the fluidwithin the cylinder is discharged to the second reservoir 4, via anoutlet 19 and a non-return valve 20. From the engaged position, movementof the piston towards the disengaged position, whereby the position iswithdrawn past the inlet, allows the cylinder 12 to re-fill with fluidreceived from the first reservoir. Continuous rotation of the swashplate 9 causes repetition of the engaged and disengaged piston cycle,thereby producing fluid flow from the first reservoir to the secondreservoir.

[0027]FIG. 5 illustrates actuation of the by-pass mechanism in thepumping system according to the invention. The by-pass 5 comprises a cam21, a cam shaft 22, a cam follower 23, a spring clutch 24 and a by-passvalve 95. The by-pass valve is coupled to the cam-follower which engagesthe cam. Rotation of the cam in a first direction of rotation causes theby-pass valve to close thereby preventing transfer of fluid from thesecond reservoir 4 to the first reservoir 3. Rotation of the cam in asecond direction of rotation allows return of the fluid from the secondreservoir to the first reservoir.

[0028] The camshaft 22 is coupled to the drive shaft 16 via a springclutch 24. Rotation of the motor 1 in the first direction causes thespring clutch to unwind, causing it to loosen its grip on the camshaft.

[0029] In FIG. 5a, initial rotation of the motor 1 in the firstdirection of rotation causes the cam 21 to rotate such that the camfollower 23 is retracted and the by-pass valve 25 is closed. Furtherrotation of the motor in the first direction causes the spring clutch 24to disengage whereby the cam and camshaft 22 are restrained by an endstop 26, and continued rotation of the motor is substantiallyunrestricted.

[0030] In FIG. 5b, rotation of the motor 1 in the second direction ofrotation causes the spring clutch 24 to engage the camshaft 22, therebyrotating the cam 21. This causes the cam-follower 23 to adapt and, as aconsequence, open the by-pass valve allowing fluid to flow back from thesecond reservoir 4 to the first reservoir 3. The valve remains openuntil pump rotation is reversed.

[0031] In one example of a system according to the invention, theoverall dimensions were 22 mm diameter and 62 mm length. The hydraulicfluid used was 10W40 motor oil which was pumped at up to 30 ml perminute at pressures of 48.3 Bar (4.8 MN/m² or 700 psi).

[0032]FIGS. 6a and 6 b show an alternative clutch arrangement which maybe used instead of the spring clutch 24. The alterative clutch 27comprises two clutch plates 28, 29, both of which have bevelled teeth30, 31. The clutch plates are urged together, preferably by springloading (not shown). FIG. 6a shows the operation of the alternativeclutch 27 corresponding to rotation of the motor 1 in the firstdirection of rotation. The bevelled teeth 30, 31 do not engage eachother, instead they react against the urging force between the clutchplates 28, 27 and allow the clutch plates to run over each other.

[0033]FIG. 6b shows the operation of the alterative clutch 27corresponding to rotation of the motor 1 in thet second direction ofrotation. Such rotation causes the bevelled teeth 30, 31 to engage,thereby preventing relative motion between the two clutch plates 28, 29.

1. A pumping system comprising a first reservoir (3) and a secondreservoir (4), a motor (1) coupled to a drive shaft (16); a pump (2),driven by the drive shaft (16), for pumping fluid from the firstreservoir (3) to the second reservoir (4) and by-pass means (5) forcontrollably returning fluid from the second reservoir (4) to the firstreservoir (3); characterised by a clutch (24;27) between the drive shaft(16) and the by-pass; means (5) whereby rotation of the drive shaft (16)in a first direction drives the pump (2) and disengages the clutch(24;27) while the by-pass means (5) is closed, and rotation of the driveshaft (16) in a second direction engage as the clutch (24;27) so thatthe by-pass means (5) is opened.
 2. A system according to claim 1,wherein the by-pass means (5) is adapted to be closed when the motor (1)is idle.
 3. A system according to claim 1 or claim 2, wherein theby-pass means (5) comprises a by-pass valve (25).
 4. A system accordingto any preceding claim, wherein the by-pass means (5) comprises acam-follower (23) and a cam (21); wherein the clutch (24;27) isoperative between the drive shaft (16) and the cam (21); and wherebyopening and closure of the by-pass means is controlled by engagement ofthe cam-follower (23) with the cam (21) and rotation of the drive shaft(16).
 5. A system according to claim 4 wherein the cam (21) comprises anend stop (26), whereby rotation of the drive shaft (16) in the seconddirection causes the end stop (26) to reach the cam-follower (23) afterthe by-pass means (5) is opened, thereby restraining the cam (21).
 6. Asystem according to any preceding claim, wherein the clutch comprises aflexible resilient sleeve (24) attached to the drive shaft (16) andadapted to grip a shaft (22) operatively associated with the by-passmeans (5) when the drive shaft (16) is rotated in the second direction;and whereby rotation of the drive shaft (16) in the first directioncauses the sleeve (24) to loosen from the second-mentioned shaft (22).7. A system according to claim 6, wherein the flexible resilient sleevecomprises a spring (24).
 8. A system according to any one of claims 1 to5, wherein the clutch comprises two clutch plates (28,29); wherein eachclutch plate (28,29) comprises bevelled teeth (30,31); wherein at leastone clutch plate is sprung loaded; whereby rotation of the drive shaft(16) in the first direction allows the bevelled teeth (30,31) to passover each other; and whereby rotation of the drive shaft (16) in thesecond direction causes the bevelled teeth (30,31) to mesh.
 9. A systemaccording to any preceding claim, wherein the by-pass means (5) ishoused within the pump (2).
 10. A system as claimed in any precedingclaim wherein the pump (2) comprises a smash plate pump.